Quartz crystal blank and quartz crystal resonator unit

ABSTRACT

A rectangular quartz crystal blank having long sides substantially parallel to a Z′ axis of the quartz crystal blank, and short sides substantially parallel to an X axis of the quartz crystal blank. The quartz crystal blank includes a first center region, a second region and a third region that are adjacent to the first region along a long-side direction, and a fourth region and a fifth region that are adjacent to the first region along a short-side direction. A thickness of the second region and a thickness of the third region are smaller than the thickness of the first region, and/or a thickness of the fourth region and a thickness of the fifth region are smaller than the thickness of the first region, and 16.18≦W/T≦16.97, where W is a length of a short side and T is a thickness.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of International applicationNo. PCT/JP2016/069854, filed Jul. 5, 2016, which claims priority toJapanese Patent Application No. 2015-137777, filed Jul. 9, 2015, theentire contents of each of which are incorporated herein by reference.

Field of the Invention

The present invention relates to an AT-cut quartz crystal blank and aquartz crystal resonator unit.

BACKGROUND OF THE INVENTION

As reduction in size of a quartz crystal resonator unit has beendemanded in recent years, it is necessary to reduce the size of a quartzcrystal blank. However, when the size of a quartz crystal blank isreduced, the influence of a sub-vibration becomes pronounced or aninfluence of vibration leakage arises, and therefore series resistancetends to increase. Examples of existing inventions related to a quartzcrystal blank and aimed at reduction of series resistance include aquartz crystal resonator plate described in Patent Document 1. Endportions of the quartz crystal resonator plate are chamfered (beveled).Thus, vibration energy is confined under excitation electrodes, andappropriate series resistance can be achieved.

As described above, regarding a quartz crystal blank, variousimprovements have been made in order to achieve appropriate seriesresistance.

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. 2013-34176

SUMMARY OF THE INVENTION

An object of the present invention is to provide a quartz crystal blankand a quartz crystal resonator unit that can reduce a crystal impedance(CI) value.

A quartz crystal blank according to an aspect of the present inventionis an AT-cut quartz crystal blank that is plate-shaped and isrectangular when seen in a direction normal to a main surface. Longsides of the main surface are substantially parallel to a Z′ axis of thequartz crystal blank. Short sides of the main surface are substantiallyparallel to an X axis of the quartz crystal blank. A frequency of a mainvibration of the quartz crystal blank is in a range of 28.5 MHz to 30.5MHz. The quartz crystal blank includes a first region including a centerof the main surface when seen in the direction normal to the mainsurface, a second region and a third region that are adjacent to thefirst region on both sides in a long-side direction in which the longsides extend, and a fourth region and a fifth region that are adjacentto the first region on both sides in a short-side direction in which theshort sides extend. A thickness of the first region is substantiallyuniform. A thickness of the second region and a thickness of the thirdregion are smaller than the thickness of the first region, and/or athickness of the fourth region and a thickness of the fifth region aresmaller than the thickness of the first region. 16.18≦W/T≦16.97 issatisfied, where W is a length of the first region, the fourth region,and the fifth region in the short-side direction, and T is the thicknessof the first region.

The present invention is also directed at a quartz crystal resonatorunit including the quartz crystal blank.

With the present invention, the CI value can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external perspective view of a quartz crystal resonatorunit 10.

FIG. 2 is an exploded perspective view of the quartz crystal resonatorunit 10.

FIG. 3 is a sectional view taken along line A-A of FIG. 1.

FIG. 4 is a sectional view taken along line B-B of FIG. 2.

FIG. 5 is a sectional view taken along line C-C of FIG. 2.

FIG. 6 is a top view of a quartz crystal blank 17.

FIG. 7 is an enlarged view of a region A1.

FIG. 8 is a graph representing the relationship between the frequenciesof a main vibration and sub-vibrations and W/T of a quartz crystal blank17 in which the frequency of the main vibration is 28.5 MHz.

FIG. 9 is a graph representing the relationship between the frequenciesof a main vibration and sub-vibrations and W/T of a quartz crystal blank17 in which the frequency of the main vibration is 30.0 MHz.

FIG. 10 is a graph representing the relationship between the frequenciesof a main vibration and sub-vibrations and W/T of a quartz crystal blank17 in which the frequency of the main vibration is 30.5 MHz.

FIG. 11 is graph representing the result of an experiment performed onfirst to third samples.

FIG. 12 is graph representing the result of an experiment performed onfourth to sixth samples.

FIG. 13 is a sectional view of a quartz crystal resonator unit 10 aaccording to a modification.

FIG. 14 is a sectional view of a quartz crystal oscillator 300.

FIG. 15 is a sectional view of a quartz crystal blank 17 a according toanother embodiment.

FIG. 16 is a sectional view of a quartz crystal blank 17 b according toanother embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(Structure of Quartz Crystal Resonator Unit)

Hereinafter, a quartz crystal resonator unit that includes a quartzcrystal blank according to an embodiment of the present invention willbe described with reference to the drawings. FIG. 1 is an externalperspective view of a quartz crystal resonator unit 10. FIG. 2 is anexploded perspective view of the quartz crystal resonator unit 10. FIG.3 is a sectional view taken along line A-A of FIG. 1.

Hereinafter, a direction normal to the main surface of the quartzcrystal resonator unit 10 is defined as the vertical direction, adirection in which the long sides of the quartz crystal resonator unit10 extend when seen from above is defined as the long-side direction,and a direction in which the short sides of the quartz crystal resonatorunit 10 extend is defined as the short-side direction.

Hereinafter, structures may be described with respect to the axialdirections of AT cut of a quartz crystal blank 17.

As illustrated in FIGS. 1 to 3, the quartz crystal resonator unit 10includes a substrate 12, a metal cap 14, a quartz crystal resonator 16,and a brazing alloy 50. The width of the short sides of the quartzcrystal resonator unit 10 is 1.6 mm, and the length of the long sides ofthe quartz crystal resonator unit 10 is 2.0 mm.

The substrate 12 (an example of a circuit substrate) includes asubstrate body 21; outer electrodes 22, 26, 40, 42, 44, and 46; via-holeconductors 25, 28, 54, and 56; and a metalized film 30.

The substrate body 21 is plate-shaped and is rectangular when seen fromabove. The substrate body 21 is made from, for example, a ceramicinsulating material, such as an aluminum oxide sintered compact, amullite sintered compact, an aluminum nitride sintered compact, asilicon carbide sintered compact, or a glass ceramic sintered compact;quartz crystal; glass; silicon; or the like. In the present embodiment,the substrate body 21 is a stack of insulating layers made of a ceramicmaterial. The substrate body 21 has an upper main surface and a lowermain surface. The upper main surface (main surface on the +Y′ side) ofthe substrate body 21 will be referred to as the “front surface”, andthe lower main surface (main surface on the −Y′ side) of the substratebody 21 will be referred to as the “back surface”.

The outer electrodes 22 and 26 are disposed on an end portion of thefront surface of the substrate body 21 in the long-side direction so asto be arranged in the short-side direction. To be specific, the outerelectrode 22 is a rectangular conductor layer that is disposed near thecorner on the −Z′ and +X side of the front surface of the substrate body21. The outer electrode 26 is a rectangular conductor layer that isdisposed near the corner on the −Z′ and −X side of the front surface ofthe substrate body 21.

The outer electrodes 40, 42, 44, and 46 are disposed near the respectivecorners of the back surface of the substrate body 21. The outerelectrode 40 is a square conductor layer that is disposed near thecorner on the −Z′ and −X side of the back surface of the substrate body21. The outer electrode 40 overlaps the outer electrode 26 when seenfrom above. The outer electrode 42 is a square conductor layer that isdisposed near the corner on the −Z′ and +X side of the back surface ofthe substrate body 21. The outer electrode 42 overlaps the outerelectrode 22 when seen from above. The outer electrode 44 is a squareconductor layer that is disposed near the corner on the +Z′ and −X sideof the back surface of the substrate body 21. The outer electrode 46 isa square conductor layer that is disposed near the corner on the +Z′ and+X side of the back surface of the substrate body 21.

The via-hole conductor 25 extends through the substrate body 21 in thevertical direction and connects the outer electrode 22 and the outerelectrode 42 to each other. The via-hole conductor 28 extends throughthe substrate body 21 in the vertical direction and connects the outerelectrode 26 and the outer electrode 40 to each other.

The metalized film 30 is a linear metal film disposed on the frontsurface of the substrate body 21. The metalized film 30 isrectangular-ring shaped when seen from above (in the direction normal tothe front surface). The outer electrodes 22 and 26 are disposed in aregion surrounded by the metalized film 30 when seen from above.

The via-hole conductor 54 extends through the substrate body 21 in thevertical direction and connects the metalized film 30 and the outerelectrode 46 to each other. The via-hole conductor 56 extends throughthe substrate body 21 in the vertical direction and connects themetalized film 30 and the outer electrode 44 to each other.

The outer electrodes 22, 26, 40, 42, 44, and 46 and the metalized film30 have a three-layer structure. To be specific, the three-layerstructure is formed by stacking a molybdenum layer, a nickel layer, anda gold layer from below. The via-hole conductors 25, 28, 54, and 56 areformed by embedding conductors, such as molybdenum, into via-holesformed in the substrate body 21.

The quartz crystal resonator 16 includes the quartz crystal blank 17,outer electrodes 97 and 98, excitation electrodes 100 and 101, andextension electrodes 102 and 103. The quartz crystal blank 17 isplate-shaped and is rectangular when seen from above. The upper mainsurface of the quartz crystal blank 17 will be referred to as the “frontsurface”, and the lower main surface of the quartz crystal blank 17 willbe referred to as the “back surface”.

The quartz crystal blank 17 is an AT-cut quartz crystal blank that iscut from, for example, a rough quartz crystal at a predetermined angle.The long sides of the front surface and the back surface of the quartzcrystal blank 17 are substantially parallel to the Z′ axis of the quartzcrystal blank 17. The short sides of the front surface and the backsurface of the quartz crystal blank 17 are substantially parallel to theX axis of the quartz crystal blank 17. Here, “substantially parallel”allows deviation within about ±1 degree relative to the Z′ axis and theX axis. The quartz crystal blank 17 is beveled, as described below indetail. In each of FIGS. 2 and 3, beveled portions are not illustrated.

The quartz crystal resonator unit is sized so that the length in thelong-side direction is 2.0 mm and the width in the short-side directionis 1.6 mm. To achieve this size, in consideration of the thickness of apackage wall, bleeding of a molding compound, and the precision ofmounting an element, the quartz crystal blank 17 is designed so as havea length of 1.500 mm or smaller in the long-side direction and a widthof 1.00 mm or smaller in the short-side direction.

The outer electrode 97 is a conductor layer that is disposed in a regionincluding the corner on the −Z′ and +X side of the quartz crystal blank17. The outer electrode 97 is formed on the front surface and the backsurface of the quartz crystal blank 17 and also on side surfaces on the+X side and the −Z′ side of the quartz crystal blank 17. The outerelectrode 98 is a conductor layer that is disposed in a region includingthe corner on the −Z′ and −X side of the quartz crystal blank 17. Theouter electrode 98 is formed on the front surface and the back surfaceof the quartz crystal blank 17 and also on side surfaces on the −X sideand the −Z′ side of the quartz crystal blank 17. Thus, the outerelectrodes 97 and 98 are arranged along a short side of the quartzcrystal blank 17.

The excitation electrode 100 is disposed at the center of the frontsurface of the quartz crystal blank 17 and is rectangular when seen fromabove. The excitation electrode 101 is disposed at the center of theback surface of the quartz crystal blank 17 and is rectangular when seenfrom above. The excitation electrode 100 and the excitation electrode101 completely overlap each other when seen from above.

The extension electrode 102 is disposed on the front surface of thequartz crystal blank 17 and connects the outer electrode 97 and theexcitation electrode 100 to each other. The extension electrode 103 isdisposed on the back surface of the quartz crystal blank 17 and connectsthe outer electrode 98 and the excitation electrode 101 to each other.The outer electrodes 97 and 98, the excitation electrodes 100 and 101,and the extension electrodes 102 and 103 are each formed, for example,by stacking a gold layer on a chrome underlying layer.

The quartz crystal resonator 16 is mounted on the front surface of thesubstrate 12. To be specific, the outer electrode 22 and the outerelectrode 97 are fixed to each other so as to be electrically connectedto each other by using an electroconductive adhesive 210, and the outerelectrode 26 and the outer electrode 98 are fixed to each other so as tobe electrically connected to each other by using an electroconductiveadhesive 212.

The metal cap 14 is a housing that has a rectangular opening. The metalcap 14 is made, for example, by plating a base metal, such as aniron-nickel alloy or a cobalt-nickel alloy, with nickel and gold. In thepresent embodiment, the metal cap 14 is a rectangular-parallelepiped boxwhose lower side is open. The metal cap 14 is made by plating a basemetal, which is an iron-nickel alloy, with nickel and gold.

The brazing alloy 50 is disposed on the metalized film 30. The brazingalloy 50 has substantially the same shape as the metalized film 30 andis rectangular-ring shaped. The brazing alloy 50 has a melting pointlower than that of the metalized film 30 and is made of, for example, agold-tin alloy. The brazing alloy 50 is formed on the metalized film 30by, for example, printing or the like. The metalized film 30 is meltedand solidified in a state in which the outer edge of the opening of themetal cap 14 is in contact with the brazing alloy 50. Thus, the metalcap 14 is joined to the metalized film 30 via the brazing alloy 50 alongthe entire length of the outer edge of the opening. As a result, thefront surface of the substrate body 21 and the metal cap 14 form ahermetically sealed space Sp. Accordingly, the quartz crystal resonator16 is contained in the hermetically sealed space Sp. Since the metal cap14 is in close contact with the substrate body 21 via the metalized film30 and the brazing alloy 50, the inside of the hermetically sealed spaceSp is maintained in a vacuum state. However, the inside may be in anatmospheric state. Instead of the brazing alloy 50, for example, anadhesive made of low-melting-point glass, a resin, or the like may beused. In this case, the metalized film 30 may be omitted.

(Details of Quartz Crystal Blank)

Hereinafter, details of the quartz crystal blank 17 will be describedwith reference to the drawings. FIG. 4 is a sectional view taken alongline B-B of FIG. 2. FIG. 5 is a sectional view taken along line C-C ofFIG. 2. FIG. 6 is a top view of the quartz crystal blank 17. FIG. 7 isan enlarged view of a region A1.

In order to reduce the CI value, the quartz crystal blank 17 accordingto the present embodiment satisfies the following conditions.

Condition 1: The frequency of a main vibration of the quartz crystalblank 17 is in the range of 28.5 MHz to 30.5 MHz.

Condition 2: The long sides of the front surface and the back surface ofthe quartz crystal blank 17 are substantially parallel to the Z′ axis ofthe quartz crystal blank 17.

Condition 3: The short sides of the front surface and the back surfaceof the quartz crystal blank 17 are substantially parallel to the X axisof the quartz crystal blank 17.

Condition 4: The quartz crystal blank 17 is beveled so that, asillustrated in FIGS. 4 and 5, the thickness of portions of the quartzcrystal blank 17 near the outer edges of the front surface and the backsurface of the quartz crystal blank 17 is smaller than the thickness ofa portion of the quartz crystal blank 17 near the centers of the frontsurface and the back surface of the quartz crystal blank 17.

Condition 5: 16.18≦W/T≦16.97 is satisfied, where W is the length ofregions A1, A4, and A5 of the quartz crystal blank 17 in the short-sidedirection, and T is the thickness of the region A1 of the quartz crystalblank 17. The regions A1, A4, and A5 will be described below.

<Regarding Condition 1>

The frequency of the main vibration of the quartz crystal blank 17depends on the thickness T of the quartz crystal blank 17. Accordingly,the thickness T of the quartz crystal blank 17 is set in the range of0.0548 mm to 0.0586 mm.

<Regarding Conditions 2 and 3>

In general, a quartz crystal blank is fixed to a substrate by bonding aportion of the quartz crystal blank near a short side thereof to thesubstrate by using an electroconductive adhesive. Moreover, it is knownthat the vibration direction of a thickness shear vibration of an AT-cutquartz crystal blank is the X-axis direction. Accordingly, an existingquartz crystal blank whose long sides are parallel to the X axis islikely to influence the substrate due to vibration leakage via theelectroconductive adhesive near the short side. In contrast, in theAT-cut quartz crystal blank 17 according to the present embodiment,vibration leakage to a Z′ axis region is small, because the long sidesare parallel to the Z′ axis. Therefore, even when the quartz crystalblank 17 is fixed to the substrate 12 by bonding a portion of the quartzcrystal blank 17 near a short side thereof by using theelectroconductive adhesives 210 and 212, the influence of vibrationleakage on the substrate 12 is small. Accordingly, with the AT-cutquartz crystal blank according to the present embodiment, the influenceof vibration leakage is smaller and the CI value is better than a quartzcrystal blank whose long sides are parallel to the X axis.

<Regarding Condition 4>

As illustrated in FIG. 6, the quartz crystal blank 17 includes regionsA1 to A5 when seen from above. The region A1 is a rectangular regionincluding the center of the front surface when seen from above. However,the shape of the region A1 may be non-rectangular when seen from aboveand may be, for example, elliptical. The region A2 is a rectangularregion adjacent to the region A1 on the +Z′ side. The region A2 is incontact with the entirety of a short side of the front surface on the+Z′ side and with end portions, in the +Z′ direction, of long sides ofthe front surface on the −X side and +X side. That is, the region A2 ispositioned at an end portion of the quartz crystal blank 17 in the +Z′direction. The region A3 is a rectangular region adjacent to the regionA1 on the −Z′ side. The region A3 is in contact with the entirety of ashort side of the front surface on the −Z′ side and with end portions,in the −Z′ direction, of the long sides of the front surface on the −Xside and +X side. That is, the region A3 is positioned at an end portionof the quartz crystal blank 17 in the −Z′ direction.

The region A4 is a rectangular region that is adjacent to the region A1on the −X side and interposed between the regions A2 and A3 from theleft and right sides. The region A4 is in contact with a portion,excluding both ends, of a long side of the front surface on the −X side.That is, the region A4 is positioned at an end portion of the quartzcrystal blank 17 in the −X direction. The region A5 is a rectangularregion that is adjacent to the region A1 on the +X side and interposedbetween the regions A2 and A3 from the right and left sides. The regionA5 is in contact with a portion, excluding both ends, of a long side ofthe front surface on the +X side. That is, the region A5 is positionedat an end portion of the quartz crystal blank 17 in the +X direction.

As illustrated in FIGS. 4 and 5, the thickness T of the region A1 issubstantially uniform. However, the front surface and back surface ofthe region A1 are slightly curved. Accordingly, as illustrated in FIG.7, the region A1 that is substantially uniform is a region having athickness in the range of (Tmax−2 μm) to Tmax, where Tmax is the maximumvalue of the thickness of the quartz crystal blank in the region A1. Theregion A1 is a region that includes the center of the front surface andthat is continuous. The thickness T of the region A1, which issubstantially uniform, has the value Tmax.

As illustrated in FIGS. 4 and 5, the thicknesses of the regions A2 to A5are smaller than the thickness T of the region A1. In the presentembodiment, the thicknesses of the regions A2 to A5 continuouslydecrease with increasing distance from the region A1. In the presentembodiment, the front surfaces and the back surfaces of the regions A2to A5 are convex surfaces.

<Regarding Condition 5>

16.18≦W/T≦16.97 is satisfied, where W is the length of the regions A1,A4, and A5 of the quartz crystal blank 17 in the short-side direction,and T is the thickness of the region A1 of the quartz crystal blank 17.Preferably, 16.51≦W/T≦16.68 is satisfied.

<Regarding Other Conditions>

Preferably, in addition to the conditions 1 to 5, 0.66≦RL/L≦0.95 issatisfied, where L is the length of the regions A1 to A3 in thelong-side direction, and RL is the length of the region A1 in thelong-side direction; and 0.69≦RW/W≦0.95 is satisfied, where RW is thelength of the region A1 in the short-side direction. More preferably,0.66≦RL/L≦0.73 is satisfied, where L is the length of the regions A1 toA3 in the long-side direction, and RL is the length of the region A1 inthe long-side direction; and 0.69≦RW/W≦0.77 is satisfied, where RW isthe length of the region A1 in the short-side direction. Here, thelength RL is the length of a portion of the region A1 extending in thelong-side direction and passing through a point in the region A1 wherethe thickness is Tmax. The length RW is the length of a portion of theregion A1 extending in the short-side direction and passing through thepoint in the region A1 where the thickness is Tmax.

(Method of Manufacturing Quartz Crystal Resonator Unit)

Hereinafter, a method of manufacturing the quartz crystal resonator unit10 will be described with reference to the drawings.

First, a method of manufacturing the substrate 12 will be described. Amother substrate in which a plurality of substrate bodies 21 arearranged in a matrix pattern is prepared. The mother substrate is madefrom, for example, a ceramic insulating material, such as an aluminumoxide sintered compact, a mullite sintered compact, an aluminum nitridesintered compact, a silicon carbide sintered compact, or a glass ceramicsintered compact; quartz crystal; glass; silicon; or the like.

Next, through-holes are formed by irradiating, with a beam, positions onthe mother substrate at which the via-hole conductors 25, 28, 54, and 56of the substrate body 21 are to be formed. Moreover, the through-holesare filled with an electroconductive material, such as molybdenum, andthe electroconductive material is dried. Subsequently, the via-holeconductors 25, 28, 54, and 56 are formed by firing the electroconductivematerial.

Next, underlying electrodes of the outer electrodes 40, 42, 44, and 46are formed on the back surface of the mother substrate. To be specific,a molybdenum layer is printed on the back surface of the mothersubstrate and dried. Subsequently, the molybdenum layer is fired. Thus,the underlying electrodes of the outer electrodes 40, 42, 44, and 46 areformed.

Next, underlying electrodes of the outer electrodes 22 and 26 and themetalized film 30 are formed on the front surface of the mothersubstrate. To be specific, a molybdenum layer is printed on the frontsurface of the mother substrate and dried. Subsequently, the molybdenumlayer is fired. Thus, the underlying electrodes of the outer electrodes22 and 26 and the metalized film 30 are formed.

Next, the underlying electrodes of the outer electrodes 40, 42, 44, 46,22, and 26 and the metalized film 30 are plated with nickel and gold inthis order. Thus, the outer electrodes 40, 42, 44, 46, 22, and 26 andthe metalized film 30 are formed.

Here, by using a vacuum printing method or the like, it is possible tosimultaneously perform filling of the through-holes with theelectroconductive material and printing of the outer electrode and thelike on the mother substrate. At this time, the electroconductivematerial, the outer electrodes, and the like are simultaneously fired.

When the mother substrate is made from a ceramic sintered compactinsulating material, while the mother substrate is in a sheet shapebefore being fired, through-holes are formed, the through-holes arefilled with the electroconductive material, and the outer electrodes 22,26, 40, 42, 44, and 46 and the metalized film 30 are printed and dried.Subsequently, a plurality of such sheets are stacked and press-bonded toform a stacked sheet. By firing the stacked sheet, it is possible tosimultaneously form the via-hole conductors; the outer electrodes 22,26, 40, 42, 44, and 46; the metalized film 30; and the substrate body21. Subsequently, plating is performed in the same way as describedabove.

Next, the mother substrate is divided into a plurality of substratebodies 21 by using a dicer. Division grooves may be formed in the mothersubstrate by irradiating the mother substrate with a laser beam, andthen the mother substrate may be divided into a plurality of substratebodies 21.

Next, a method of manufacturing the quartz crystal resonator 16 will bedescribed. The quartz crystal blank 17, which is rectangularplate-shaped, is obtained by AT-cutting a rough quartz crystal. At thistime, the rough quartz crystal is cut so that the long sides of thefront surface and the back surface of the quartz crystal blank 17 aresubstantially parallel to the Z′ axis of the quartz crystal blank 17 andthe short sides of the front surface and the back surface of the quartzcrystal blank 17 are substantially parallel to the X axis of the quartzcrystal blank 17.

Next, the quartz crystal blank 17 is beveled by using a barrel finishingapparatus. Thus, ridge portions of the quartz crystal blank 17 areground, and, as illustrated in FIGS. 4 and 5, the quartz crystal blank17 has a cross-sectional shape such that the thickness thereof decreaseswith increasing distance from the center of the front surface.

Next, the outer electrodes 97 and 98, the excitation electrodes 100 and101, and the extension electrodes 102 and 103 are formed on the quartzcrystal blank 17. Since the outer electrodes 97 and 98, the excitationelectrodes 100 and 101, and the extension electrodes 102 and 103 can beformed through a general process, the description of the process will beomitted.

Next, the quartz crystal resonator 16 is mounted on the front surface ofthe substrate body 21. To be specific, as illustrated in FIGS. 2 and 3,the outer electrode 22 and the outer electrode 97 are bonded to eachother by using the electroconductive adhesive 210, and the outerelectrode 26 and the outer electrode 98 are bonded to each other byusing the electroconductive adhesive 212.

Next, the metal cap 14 is attached to the substrate 12 by using thebrazing alloy 50. Through the process described above, the quartzcrystal resonator unit 10 is completed.

(Advantageous Effects)

With the quartz crystal blank 17 and the quartz crystal resonator unit10 according to the present embodiment, the CI value can be reduced. Tobe more specific, as illustrated in FIGS. 4 and 5, the quartz crystalblank 17 has a sectional shape such that the thickness thereof decreaseswith increasing distance from the center of the front surface. Thus, thevibration energy of the main vibration of the quartz crystal blank 17 isconfined in the region A1. The excitation electrodes 100 and 101 aredisposed on the region A1. As a result, the main vibration isefficiently converted into an electric signal, and the electric signalis output from the excitation electrodes 100 and 101. Thus, with thequartz crystal blank 17 and the quartz crystal resonator unit 10, the CIvalue can be reduced.

With the quartz crystal blank 17 and the quartz crystal resonator unit10, the CI value can be reduced also for the following reasons. FIG. 8is a graph representing the relationship between the frequencies of amain vibration and sub-vibrations and W/T of a quartz crystal blank 17in which the frequency of the main vibration is 28.5 MHz. FIG. 9 is agraph representing the relationship between the frequencies of a mainvibration and sub-vibrations and W/T of a quartz crystal blank 17 inwhich the frequency of the main vibration is 30.0 MHz. FIG. 10 is agraph representing the relationship between the frequencies of a mainvibration and sub-vibrations and W/T of a quartz crystal blank 17 inwhich the frequency of the main vibration is 30.5 MHz. In each of FIGS.8 to 10, the triangles represent the main vibration, and the squares andthe rhombuses represent the sub-vibrations.

In the quartz crystal blank 17 and the quartz crystal resonator unit 10,sub-vibrations occur in addition to a main vibration. The main vibrationis a thickness shear vibration. The frequency of the main vibrationdepends on the thickness T of the quartz crystal blank 17. Thesub-vibrations, which are vibrations other than the main vibration,occur due to extension and contraction of the quartz crystal blank 17 inthe short-side direction, extension and contraction of the quartzcrystal blank 17 in the long-side direction, warping of the quartzcrystal blank 17, and the like. The frequencies of the sub-vibrationsdepend on the length L, the width W, and the like. Such sub-vibrationsare so-called spurious vibrations. As can be understood from the resultsof simulation described below, in which W/T was changed while keepingthe length L of the quartz crystal blank 17 in the long-side directionconstant, sub-vibrations that may occur in the quartz crystal blank 17and the quartz crystal resonator unit 10 can be suppressed by adjustingW/T.

Here, the CI value of the quartz crystal blank 17 and of the quartzcrystal resonator unit 10 can be reduced by designing the quartz crystalblank 17 and the quartz crystal resonator 16 so as to separate thefrequency of the main vibration from the frequencies of thesub-vibrations. The inventors studied the relationship between W/T andthe frequencies of the main vibration and the sub-vibrations byperforming computer simulation. In the computer simulation, for threetypes of quartz crystal blanks 17 having main vibration frequencies of28.5 MHz, 30.0 MHz, and 30.5 MHz, the width W was changed while keepingthe thickness T constant. The simulation conditions are as follows.

-   -   (1) 28.5 MHz    -   thickness T: 0.0586 mm    -   length L: 1.335 mm    -   length RL: 0.890 mm    -   RW/W: 0.73    -   (2) 30.0 MHz    -   thickness T: 0.0557 mm    -   length L: 1.335 mm    -   length RL: 0.890 mm    -   RW/W: 0.73    -   (3) 30.5 MHz    -   thickness T: 0.0548 mm    -   length L: 1.335 mm    -   length RL: 0.890 mm    -   RW/W: 0.73

By performing simulation under the above conditions, the results shownin FIGS. 8 to 10 were obtained. Then, the inventors investigatedpreferable W/T on the basis of the simulation results.

As can be seen from FIG. 8, when the frequency of the main vibration is28.5 MHz, the main vibration and sub-vibrations 1 and 2 do not intersectif W/T is in the range of 16.18 to 16.97. That is, if W/T is in therange of 16.18 to 16.97 (that is, T is 0.0586 mm and W is in the rangeof 0.948 mm to 0.994 mm), the frequency of the main vibration isseparated from the frequencies of the sub-vibrations.

As can be seen from FIG. 9, when the frequency of the main vibration is30.0 MHz, the main vibration and the sub-vibrations 1 and 2 do notintersect if W/T is in the range of 16.18 to 16.97. That is, if W/T isin the range of 16.18 to 16.97 (that is, T is 0.0557 mm and W is in therange of 0.901 mm to 0.945 mm), the frequency of the main vibration isseparated from the frequencies of the sub-vibrations.

As can be seen from FIG. 10, when the frequency of the main vibration is30.5 MHz, the main vibration and the sub-vibrations 1 and 2 do notintersect if W/T is in the range of 16.18 to 16.97. That is, if W/T isin the range of 16.18 to 16.97 (that is, T is 0.0548 mm and W is in therange of 0.886 mm to 0.929 mm), the frequency of the main vibration isseparated from the frequencies of the sub-vibrations.

These results show that, when the frequency of the main vibration of thequartz crystal blank 17 is in the range of 28.5 MHz to 30.5 MHz, thefrequency of the main vibration is separated from the frequencies of thesub-vibrations if 16.18≦W/T≦16.97. Thus, in the quartz crystal blank 17in which the frequency of the main vibration is in the range of 28.5 MHzto 30.5 MHz, the CI value can be reduced if 16.18≦W/T≦16.97.

Since a main vibration and sub-vibrations can be individually analyzedby using simulation, simulation has an advantage in that a range inwhich the influence of sub-vibrations on a main vibration in the rangeof 28.5 MHz to 30.5 MHz can be obtained by using the CI value. However,by measuring the CI values of actual samples, although only the CI valuein which a main vibration and sub-vibrations are superposed can beobtained, it is possible to obtain detailed measurement results thatreflect actual variations in dimensions, shapes, materialcharacteristics, and the like. Therefore, the inventors performed anexperiment using samples that were actually made as described below, andobtained a more preferable range of W/T in the frequency range of 28.5MHz to 30.5 MHz. To be more specific, the inventors made forty pieces ofeach of first to third samples of the quartz crystal resonator unit 10.The conditions for the first to third samples are as follows.

First to third samples (frequency of main vibration: 30.0 MHz)

TABLE 1 First Sample Second Sample Third Sample T [mm] 0.0557 0.05570.0557 L [mm] 1.355 1.355 1.355 RL [mm] 0.940 0.940 0.940 W [mm] 0.9190.924 0.929 RW [mm] 0.674 0.678 0.682

For each of the first to third samples, the CI value was measured. Inthe experiment, the ambient temperature was changed from −30° C. to 85°C. As the CI value, the maximum value for each sample when thetemperature was changed from −30° C. to 85° C. was used.

FIG. 11 is a graph representing the result of the experiment performedon the first to third samples (the frequency of the main vibration: 30.0MHz). In FIG. 11, the vertical axis represents the CI value, and thehorizontal axis represents the width W.

FIG. 11 shows measurements of the CI value for W in the range of 0.919mm to 0.929 mm where the CI value was smaller than or equal to 50 Ω,which is about twice the minimum average CI value of 26 Ω, in the casewhere the frequency of the main vibration was 30.0 MHz. In the casewhere the thickness T, which is determined from the frequency of themain vibration, was 0.0557 mm, the CI value was smaller than or equal to50 Ω and sufficiently low when W/T was in the range of 16.51 to 16.68.

Next, the inventors performed an experiment as described below andobtained preferable ranges of RL/L and RW/W. To be more specific, fortypieces of each of fourth to sixth samples were made. Conditions for thefourth to sixth samples were as follows.

Fourth to sixth samples (frequency of main vibration: 30.0 MHz)

TABLE 2 Fourth Sample Fifth Sample Sixth Sample T [mm] 0.0557 0.05570.0557 L [mm] 1.355 1.355 1.355 RL [mm] 0.890 0.940 0.990 W [mm] 0.9240.924 0.924 RW [mm] 0.642 0.678 0.714

For each of the fourth to sixth samples, the CI value was measured. Inthe experiment, the ambient temperature was changed from −30° C. to 85°C. As the CI value, the maximum value for each sample when thetemperature was changed from −30° C. to 85° C. was used.

FIG. 12 is a graph representing the result of the experiment performedon the fourth to sixth samples (the frequency of the main vibration:30.0 MHz). In FIG. 12, the vertical axis represents the CI value, andthe horizontal axis represents RL/L and RW/W.

FIG. 12 shows measurements of the CI value for RW/W in the range of 0.69to 0.77 and RL/L in the range of 0.66 to 0.73 where the CI value wassmaller than or equal to 50 Ω, which is about twice the minimum averageCI value of 26 Ω, in the case where the frequency of the main vibrationwas 30.0 MHz.

However, from FIG. 12, it is considered that the CI value can be set ina range such that the quartz crystal resonator unit can oscillate evenif RW/W is greater than 0.77 and RL/L is greater than 0.73. Therefore,in the case where the frequency of the main vibration of the quartzcrystal blank 17 is 30.0 MHz, if 0.66≦RL/L≦0.95 and 0.69≦RW/W≦0.95, theCI value can be set in a range such that the quartz crystal resonatorunit can oscillate, even though the CI value becomes high. The upperlimit of RL/L and RW/W is set at 0.95 because, if RL/L and RW/W aregreater than 0.95, the vibration energy of the main vibration of thequartz crystal blank 17 cannot be sufficiently confined in the regionA1.

(Modification)

Hereinafter, a quartz crystal resonator unit 10 a according to amodification will be described with reference to the drawings. FIG. 13is a sectional view of the quartz crystal resonator unit 10 a accordingto the modification.

As illustrated in FIG. 13, the quartz crystal resonator unit 10 aaccording to the present modification includes a quartz crystalresonator 16 including a quartz crystal blank 17, and differs from thequartz crystal resonator unit 10 according to the embodiment describedabove in that a thermistor 60 is disposed on a back surface of asubstrate 12. As the quartz crystal blank 17, a quartz crystal blankaccording to the embodiment described above can be used.

(Quartz Crystal Oscillator)

Hereinafter, a quartz crystal oscillator 300 including a quartz crystalblank 17 will be described with reference to the drawings. FIG. 14 is asectional view of the quartz crystal oscillator 300.

As illustrated in FIG. 14, the quartz crystal oscillator 300 includes aquartz crystal resonator 16 including the quartz crystal blank 17, anddiffers from the quartz crystal resonator unit 10 shown in FIG. 3 inthat an IC 302 is mounted on a back surface of a substrate 12. As thequartz crystal blank 17, a quartz crystal blank according to theembodiment described above can be used.

Other Embodiments

A quartz crystal blank and a quartz crystal resonator unit according tothe present invention are not limited to the quartz crystal blank 17 andthe quartz crystal resonator unit 10, and may be modified within thescope of the present invention.

The quartz crystal blank 17 has a shape such that the thickness thereofdecreases with increasing distance from the center of the front surfacein the short-side direction and in the long-side direction. However, thethickness of the quartz crystal blank 17 may decrease with increasingdistance from the center of the front surface in the short-sidedirection or may decrease with increasing distance from the center ofthe front surface in the long-side direction. That is, it is sufficientthat the thickness of the region A2 and the thickness of the region A3are smaller than the thickness of the region A1 and/or the thickness ofthe region A4 and the thickness of the region A5 are smaller than thethickness of the region A1.

FIGS. 15 and 16 are sectional views of quartz crystal blanks 17 a and 17b according to other embodiments. As illustrated in FIG. 15, a regionhaving a larger thickness than the region A2 may be disposed on the +Z′side of the region A2; and a region having a larger thickness than theregion A3 may be disposed on the −Z′ side of the region A3. Likewise, aregion having a larger thickness than the region A4 may be disposed onthe −X side of the region A4. A region having a larger thickness thanthe region A5 may be disposed on the +X side of the region A5. That is,as long as the region A2 to A5, each of which has a smaller thicknessthan the region A1, are disposed around the region A1, vibration energyof a main vibration is confined in the region A1. Therefore, otherregions may be present or may not be present around the regions A2 toA5.

The regions A2 to A5, which have continuously-changing convex surfaces,may have concave surfaces or discontinuously-changing surfaces. That is,as illustrated in FIG. 16, the regions A2 to A5 may have step-likeshapes.

As described above, the present invention can be used for a quartzcrystal blank and a quartz crystal resonator unit and, in particular,advantageous in that the CI value can be reduced.

REFERENCE SIGNS LIST

-   10, 10 a quartz crystal resonator unit-   12 substrate-   14 metal cap-   16 quartz crystal resonator-   17, 17 a, 17 b quartz crystal blank-   21 substrate body-   22, 26, 40, 42, 44, 46 outer electrode-   30 metalized film-   50 brazing alloy-   60 thermistor-   100, 101 excitation electrode-   300 quartz crystal oscillator-   A1 to A5 region

1. An AT-cut quartz crystal blank comprising: a quartz crystal body thatis rectangular in shape in a direction normal to a main surface thereof,the quartz crystal body having a first region including a center of themain surface in the direction normal to the main surface, a secondregion and a third region that are adjacent to the first region onopposed sides thereof along a long-side direction in which long sides ofthe quartz crystal body extend, and a fourth region and a fifth regionthat are adjacent to the first region on opposed sides thereof along ashort-side direction in which short sides of the quartz crystal bodyextend, wherein the long sides of the main surface are substantiallyparallel to a Z′ axis of the quartz crystal blank, wherein the shortsides of the main surface are substantially parallel to an X axis of thequartz crystal blank, wherein a frequency of a main vibration of thequartz crystal blank is in a range of 28.5 MHz to 30.5 MHz, wherein athickness of the first region is substantially uniform, wherein at leastone of (1) a thickness of the second region and a thickness of the thirdregion are smaller than the thickness of the first region, and (2) athickness of the fourth region and a thickness of the fifth region aresmaller than the thickness of the first region, and wherein16.18≦W/T≦16.97, where W is a length of the first region, the fourthregion, and the fifth region along the short-side direction, and T isthe thickness of the first region.
 2. The quartz crystal blank accordingto claim 1, wherein 16.51<W/T<16.68.
 3. The quartz crystal blankaccording to claim 1, wherein the thickness of the second region and thethickness of the third region are smaller than the thickness of thefirst region, and the thickness of the fourth region and the thicknessof the fifth region are smaller than the thickness of the first region.4. The quartz crystal blank according to claim 1, wherein the thicknessof the second region and the thickness of the third region are smallerthan the thickness of the first region.
 5. The quartz crystal blankaccording to claim 1, wherein the thickness of the fourth region and thethickness of the fifth region are smaller than the thickness of thefirst region.
 6. The quartz crystal blank according to claim 3, whereinthe second region and the third region are positioned at opposed ends ofthe quartz crystal blank in the long-side direction, and wherein thefourth region and the fifth region are positioned at opposed ends of thequartz crystal blank in the short-side direction.
 7. The quartz crystalblank according to claim 6, wherein a thickness of the quartz crystalblank decreases with increasing distance from the center of the mainsurface in the long-side direction and decreases with increasingdistance from the center of the main surface in the short-sidedirection.
 8. The quartz crystal blank according to claim 6, wherein athickness of the quartz crystal blank decreases with increasing distancefrom the center of the main surface in the long-side direction.
 9. Thequartz crystal blank according to claim 6, wherein a thickness of thequartz crystal blank decreases with increasing distance from the centerof the main surface in the short-side direction.
 10. The quartz crystalblank according to claim 6, wherein 0.66≦RL/L≦0.95, where L is a lengthof the first region, the second region, and the third region along thelong-side direction, and RL is a length of the first region along thelong-side direction, and wherein 0.69≦RW/W≦0.95, where RW is a length ofthe first region along the short-side direction.
 11. The quartz crystalblank according to claim 10, wherein 0.66≦RL/L≦0.73, and wherein0.69≦RW/W≦0.77.
 12. A quartz crystal resonator unit comprising: thequartz crystal blank according to claim
 1. 13. The quartz crystalresonator unit according to claim 12, comprising: a first outerelectrode and a second outer electrode that are each arranged along arespective short side of the quartz crystal blank; a substrate body; anda third outer electrode and a fourth outer electrode that are eachdisposed on a respective main surface of the substrate body, wherein thefirst outer electrode and the third outer electrode are electricallyconnected to each other, and the second outer electrode and the fourthouter electrode are electrically connected to each other.
 14. The quartzcrystal resonator unit according to claim 13, further comprising: a capdisposed on the substrate body and covering the quartz crystalresonator.